Micro-machined or micro-electro-mechanical systems (MEMS) devices, where there is repeated physical contact between moving parts, require lubrication to prevent the onset of stiction (static friction). This stiction can be strong enough to cause the parts to stick together irreversibly, making the devices inoperable.
For example, in the digital micromirror device (DMD™) of FIG. 1, which is a type of MEMS device, a potential difference between yoke address electrodes 107 and the yoke 101 (and between mirror address electrodes 108 and the mirror 100) cause the mirror/yoke assemblies 100/101 to rotate on torsion hinges 102 attached to support posts 103 until the yoke tips 104 contact landing pads 105 located on a lower layer of the device on top of the substrate 106. It is this mechanical contact between the yoke landing tips and the landing pad sites that is of particular relevance to this invention. In some cases the mirror/yoke assemblies become slow in lifting off the landing pad, affecting the response of the device and in other cases the assemblies become permanently stuck to the landing pads. One of the primary causes of stiction has been shown to be that of the landing tips scrubbing into the metal landing pads.
By passivating (lubricating) the contact surfaces of the MEMS devices to make them “slick,” this sticking problem can be essentially eliminated over long operating times. However, a problem has been that of uniformly applying the lubricant to the device, thereby resulting in a considerable reduction in the lifetime of the devices. Also, the cost of applying the passivant can considerably impact the final device cost. What is needed is an effective passivation method that exposes the MEMS device to a mist of tiny lubricant droplets, which are deposited uniformly over the device. The method and apparatus of the present invention meets this need.